INTRODUCTION TO NANOMATERIALS

Introduction Nano materials are cornerstones of nano science and nanotechnology. Nanostructure science and technology is a broad and interdisciplinary area of research and development activity that has been growing explosively worldwide in the past few years. It has the potential for revolutionizing the ways in which materials and products are created and the range and nature of functionalities that can be accessed. It is already having a significant commercial impact, which will assuredly increase in the future.

What Are Nanomaterials

Nanoscale materials are defined as a set of substances where at least one dimension is less than approximately 100 nanometers. A nanometer is one millionth of a millimeter - approximately 100,000 times smaller than the diameter of a human hair.

Nanomateriales are of interest because at this scale unique optical, magnetic, electrical, and other properties emerge. These emergent properties have the potential for great impacts in electronics, medicine, and other fields.

Where Are Nanomaterials Found?

Some nanomaterials occur naturally, but of particular interest are engineered nanomaterials (EN), which are designed for, and already being used in many commercial products and processes. They can be found in such things as sunscreens, cosmetics, sporting goods, stain-resistant clothing, tires, electronics, as well as many other everyday items, and are used in medicine for purposes of diagnosis, imaging and drug delivery. Engineered nanomaterials are resources designed at the molecular (nanometre) level to take advantage of their small size and novel properties which are generally not seen in their conventional, bulk counterparts

Because the size of the particles is a critical factor, the material properties significant differ at the nanoscale from that at larger scales. Physical phenomena begin to occur differently below the boundary limit: gravity becomes unimportant, electrostatic forces and quantum effects start to prevail.In the same time, the proportion of atoms on the surface increases relative to those inside, creating so-called “nano-effect”. All these nano-properties actually affect the materials behavior at macro-scale and, from this point, the power of nanotechnology is emphasized: if the elements are proper manipulated at the nanoscale, the macro-properties are affected and new materials and processes can be developed (Ge & Gao, 2008). In what follows the most important nanomaterials with potential use in construction are presented.

Zinc Oxide Nanoparticles (ZnO)

Silver Nanoparticles (Ag)

Aluminum Oxide Nanoparticles (Al2O3)

Zirconium Oxide Nanoparticles (ZrO2)

Wolfram (Tungsten) Oxide Nanoparticles (WO3)

The Carbon Nanotubes

Titanium Dioxide Nanoparticles (TiO2)

Silicon Dioxide Nanoparticles (SiO2)

Carbon nanotubes are a form of carbon having a cylindrical shape, the name coming from their nanometre diameter. They can be several millimetres in length and can have one “layer” or wall (single walled nanotube) or more than one wall (multi walled nanotube) (Lu et al., 2010). Nanotubes are members of the fullerene structural family and exhibit extraordinary strength and unique electrical properties, being efficient thermal conductors. For example, they have five times the Young’s modulus and eight times (theoretically 100 times) the strength of steel, whilst being 1/6th the density. Expected benefits of carbon nanotubes are: mechanical durability and crack prevention in concrete, enhanced mechanical and thermal properties in ceramics and real-time structural health monitoring capacity (Mann, 2006).

The titanium dioxide nanoparticles are added to concrete to improve its properties. This white pigment is used as an excellent reflective coating. Or added to paints, cements and windows for its sterilizing properties. The titanium dioxid breaks down organic pollutants, volatile organic compounds and bacterial membranes through powerful photocatalytic reactions, reducing air pollutants when it’s applied to outdoor surfaces. Being hydrophilic gives self cleaning properties to surfaces to which it is applied, because the rain water is attracted to the surface and forms sheets which collect the pollutants and dirt particles previously broken down and washes them off. The resulting concrete surface has a white colour that retains its whiteness very effectively (Mann,2006).

Titanium Dioxide Nanoparticles (TiO2)

Nano-SiO2 could significantly increase the compressive strength of concretes containing large fly ash volume at early age, by filling the pores between large fly ash and cement particles. Nano-silica decreases the setting time of mortar when compared with silica fume (microsilica) and reduces bleeding water and segregation by the improvement of the cohesiveness (Sadrmomtazi & Barzegar, 2010).

Silicon Dioxide Nanoparticles (SiO2)

Zinc oxide is a unique material that exhibits semiconducting and piezoelectric dual properties. It is added into various materials and products,including plastics, ceramics, glass, cement, rubber, paints, adhesive, sealants,pigments, fire retardants. Used for concrete manufacturing, ZnO improves the processing time and the resistance of concrete against water (Broekhuizen & Broekhuizen, 2009).

Zinc Oxide Nanoparticles (ZnO)

The nanosilver will affect, in contact with bacteria, viruses and fungi,the cellular metabolism and inhibit cells growth. The nanosilver inhibits multiplication and growth of bacteria and fungi, which causes infection, odour, itchiness and sores. The core technology of nanosilver is the ability to produce particles as small as possible and to distribute these particles very uniformly. When the nanoparticles are coated on the surface of any material, the surface area is increasing several million times than the normal silver foil (www.nanosilver.com.my).

Silver Nanoparticles (Ag)

Alumina (Al2O3) component reacts with calcium hydroxide produced from the hydration of calcium silicates. The rate of the pozzolanic reaction is proportional to the amount of surface area available for reaction. The addition of nano-Al2O3 of high purity improves the characteristics of concretes, in terms of higher split tensile and flexural strength. The cement could be advantageously replaced in the concrete mixture with nano-Al2O3 particles up to maximum limit of 2.0% with average particle sizes of 15 nm, the optimal level of nano- Al2O3 particles content being achieved with 1.0% replacement (Nazariet al., 2010).

Aluminum Oxide Nanoparticles (Al2O3)

Zirconium oxide (or Zirconia) nanopowder or nanoparticles are white high surface area particles with typical dimensions of 5…100 nanometers and specific surface area in the 25…50 m2/g range. Nano zirconium shows good aesthetics (translucency), superior physical resistance (hardness, flexibility,durability), chemical resistance (practically inert) and is a very good insulator.

Zirconium Oxide Nanoparticles (ZrO2)

In recent years, tungsten trioxide has been employed in the production of electrochromic windows, or smart windows. These windows are electrically switchable glass that change light transmission properties with an applied voltage. This allows the user to tint their windows, changing the amount of heat or light passing through.

Wolfram (Tungsten) Oxide Nanoparticles (WO3)

The analysis of patenting activity pertaining to nanotechnology applications incement industry resulted in 368 patents. Figure 1 depicts the patentingtrend in the field of nanotechnology applications in cement industry. A sharpincrease in year wise publication of granted/published patents can beobserved from 2007 onwards due to the commercial success in usingnano‐scale materials as cementitious ingredients. The tally of 154 grantedpatents from a total list of 368 patents clearly shows a high output ofcommercialization and research in this field.

Disadvantages of Nanomaterials

(i) Instability of the particles (ii) Impurity

(iii) Biologically harmful

Well dispersed nano particles increase the viscosity of the liquid phase, improves the segregation resistance and workability of the system.

Accelerates the hydration.

Better bond between aggregates and cement paste.

Improves the toughness,shear,tensilestrength and flexural strength of concrete.

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